For at least some clients, the price climbed by roughly 25%, one of the people said.

'In light of the increased risks in markets, it’s sensible to expect a higher premium in order to continue to keep the lights on,' said Javier Paz, a senior analyst at Aite Group LLC.

Foreign-exchange prime brokerages provide clearing, settlement and financing for clients such as hedge funds, high-frequency-trading firms and retail foreign-exchange brokers. Once an institution has a prime-brokerage account it can trade anywhere that accepts the prime broker and will transact under that broker’s name.

The price increase means a client paying $1 for every $1 million traded would now be charged $1.25 instead.

Margins - the amount of collateral banks require in case a counterparty fails to pay - also have increased, making trades more expensive, two people said.